Re: [PATCH v11 8/8] vhost: use vhost_tasks for worker threads

[Oleg Nesterov]

On 05/16, Eric W. Biederman wrote:
>
> A kernel thread can block SIGKILL and that is supported.
>
> For a thread that is part of a process you can't block SIGKILL when the
> task is part of a user mode process.

Or SIGSTOP. Another thread can call do_signal_stop()->signal_wake_up/etc.

> There is this bit in complete_signal when SIGKILL is delivered to any
> thread in the process.
>
> 			t = p;
> 			do {
> 				task_clear_jobctl_pending(t, JOBCTL_PENDING_MASK);
> 				sigaddset(&t->pending.signal, SIGKILL);
> 				signal_wake_up(t, 1);
> 			} while_each_thread(p, t);

That is why the latest version adds try_set_pending_sigkill(). No, no,
it is not that I think this is a good idea.

> For clarity that sigaddset(&t->pending.signal, SIGKILL);  Really isn't
> setting SIGKILL pending,

Hmm. it does? Nevermind.

> The important part of that code is that SIGNAL_GROUP_EXIT gets set.
> That indicates the entire process is being torn down.

Yes. and the same is true for io-thread even if it calls get_signal()
and dequeues SIGKILL and clears TIF_SIGPENDING.

> but in that case the vhost logic needs to act like a process, just
> like io_uring does.

confused... create_io_thread() creates a sub-thread too?

Although I never understood this logic. I can't even understand the usage
of lower_32_bits() in create_io_thread().

Oleg.